1. Field of the Invention
This invention relates to improved cathodes for use with electrolytic cells used in the electrolysis of aqueous alkali metal halide solution for the production of halogen and caustic or alkali metal hypohalides.
2. Description of the Prior Art
The electrolysis of aqueous alkali metal halide solution such as solutions of sodium chloride or potassium chloride is conducted on a vast commercial scale. The electrolysis of alkali metal chlorides to produce elemental chlorine and alkali metal hydroxides is conducted in two general types of cells--the diaphragm and the mercury cathode cell. In the diaphragm cell, the cell is divided into two compartments--the anode compartment and the cathode compartment--which are separated by a porous or semiporous diaphragm which is usually made of asbestos or by an ion exchanger type membrane. The cathode is of perforated metal and the asbestos diaphragm is in contact with the cathode. The anode, which until recently was usually made of carbon or graphite, is disposed centrally in the anode compartment.
In the production of alkali metal hypochlorite and chlorate, anodes and cathodes (or bipolar electrodes which when arranged in a spaced electrical series in an electrolytic cell may serve as both anode and cathode) are submerged in an aqueous solution of the sodium chloride or the like and an electrical potential is established between the electrodes. In the past, graphite or carbon electrodes have been used as anodes or as the bipolar electrodes in series. In consequence of the electrochemical reactions which occur, alkali metal chlorate is produced either directly in the cell or outside the cell after the solution is allowed to stand.
In operating each of the above-described cells one was confronted with a common problem, namely, that during the course of the electrolysis, the carbon or graphite electrode gradually eroded or decomposed. Consequently, great interest was developed in a dimensionally stable anode that would be free of the objectionable characteristics of the graphite or carbon electrode. The dimensionally stable anodes which were developed are typically of titanium or similar valve metal and coated with a platinum metal or ruthenium oxide or alone or in combination with other oxide compounds. During the development of the improved anodes for the various electrolytic cells little or no attention has been given to the cathode employed in the cells which, as mentioned above, typically is a ferrous metal material.
Improvement in the cathode is desirable inasmuch as there is a voltage loss at the cathode in addition to a voltage loss at the anode of these electrolytic cells. Inasmuch as these cells consume tremendous amounts of electricity even a small amount, such as a tenth of a volt, of savings in electrical energy at either the cathode or the anode is of tremendous economic advantage and importance to the producer. Hindering the desire for better cathodes is the fact that the operating conditions of the cathode, e.g., high caustic concentration, heat, conductivity requirements and the like, are very deleterious to many materials which might otherwise be considered for such use.